Thread tensioning mechanism for a sewing machine

ABSTRACT

The present invention relates to a thread tensioning mechanism for a sewing machine. The mechanism is intended to obviate the problem of fatigue which normally occurs in such mechanisms, as a result of extended use of the machine. The tension regulating member of the machine is thus enabled to retain its accuracy through substantially the life of the machine. The tensioning mechanism comprises thread engaging means adapted to generate thread tension by providing resistance to the movement of a thread therethrough in proportion to a force applied to said thread engaging means and means for developing and applying said force thereto. The means for developing said force and for applying same to said thread engaging means comprises magnetically interacting elements, one of which is carried by a lever operatively connected to said thread engaging means, and the other of which is carried shiftably by operator influenced means, whereby said other element may be selectively positioned relative to the fulcrum of the lever to vary the thread tension. The present invention relates to a thread tensioning mechanism for a sewing machine and more particularly to a tensioning mechanism for the needle thread of such sewing machine.

United States Patent [191 Ketterer [4 1 Jan. 15, 11974 THREAD TENSIONING MECHANISM FOR A SEWING MACHINE [75] Inventor: Stanley J. Ketterer, Jamesburg, NJ.

[73] Assignee: The Singer Company, New York,

221 Filed: Nov. 13,1972

21 Appl. No.: 306,091

3,372,888 3/1968 Eppendahl 242/150 M Primary Examiner-George H. Krizmanich Atl0rney-Marshall .l. Breen, C. A. Williams, Jr. and Joel Halpern [57] ABSTRACT The present invention relates to a thread tensioning mechanism for a sewing machine. The mechanism is intended to obviate the problem of fatigue which normally occurs in such mechanisms, as a result of extended use of the machine. The tension regulating member of the machine is thus enabled to retain its accuracy through substantially the life of the machine. The tensioning mechanism comprises thread engaging means adapted to generate thread tension by providing resistance to the movement of a thread therethrough in proportion to a force applied to said thread engaging means and means for developing and applying said force thereto. The means for developing said force and for applying same to said thread engaging means comprises magnetically interacting elements, one of which is carried by a lever operatively connected to said thread engaging means, and the other of which is carried shiftably by operator influenced means, whereby said other element may be selectively positioned relative to the fulcrum of the lever to vary the thread tension.

The present invention relates to a thread tensioning mechanism for a sewing machine and more particularly to a tensioning mechanism for the needle thread of such sewing machine.

7 Claims, 3 Drawing Figures THREAD TENSIONING MECHANISM FOR A SEWING MACHINE BACKGROUND OF THE INVENTION It has heretofore been conventional to subject the needle thread of a sewing machine to a predetermined tension in order to produce a stitch having the proper tightness. The use of a dial selector to set the desired tension value into the machine is also well known. The magnitude of the thread tension should, once initially set at the desired value, remain constant throughout the work cycle and until the setting on the machine is reset. The dial selector enables the operator to select a value within the prescribed range established for the machine that is optimum for the particular stitch to be employed.

Tensioning mechanisms are known, such as a thread engaging device, which includes a plurality of friction discs or washers adapted to be moved relative to each other so as to subject the thread directed therebetween to increased or decreased frictional force and a concomitant increased or decreased tension.

Various arrangements have been resorted to for effectuating the relative movement between the discs or washers. One such expedient involves the mounting of such discs upon a common elongated member such as a rod or shaft. Axial displacement of the said member results in a corresponding movement of one or more of the discs and the regulation of the thread tension. The rod or shaft may be axially displaced by the application of a force to one end of a force-transmitting lever arm and the pivotal movement of the other end of the lever arm such that it acts upon the rod or shaft to thereby cause its axial displacement.

Spring means have customarily been employed to develop the force to be applied to the thread engaging means. This has occasioned certain well known diffrculties. For example, springs are subject to fatigue and a resultant change in spring constant through use over an extended period of time. Continual adjustment of the setting of the dial selector has thus been made necessary. Equally important is the fact that the springs of different machines suffer from fatigue at different rates so that the calibration of no two machines can be expected to remain the same for any length of time. This unreliability factor has been a source of annoyance to sewing machine operators; however, to date there has been no satisfactory solution of this problem. Furthermore, quite apart from the effect of fatigue upon the springs, it is recognized that the mass production of springs with exactly the same spring constant is practically impossible. Thus, even before the effect of fatigue upon the spring has taken place, the calibration of thread tensions have an inherent variation machine to machine albeit the dial selectors of such machines have been set for theoretically identical ranges of thread tensron.

SUMMARY OF THE INVENTION It is, therefore, one object of the present invention to provide a needle thread tensioning mechanism for a sewing machine in which the thread tensioning force is developed by means not subject to fatigue over an extended period of usage.

' It is another object of this invention to provide a needle thread tensioning mechanism for a sewing machine in which an operator-controlled dial selector is incorporated which, once initially calibrated to establish the thread tensioning range for the machine, will maintain its accuracy throughout the life of the machine.

A further object of the invention is to provide a needle thread tensioning mechanism for like sewing machines which permits the establishment of identically calibrated actual thread tension ranges for such machines so that an operator may select a tension value on any of such machines by the setting of the dial selector with confidence that the same actual thread tension can be set into any other such machine by setting the dial selector at the same calibrated value.

Other objects and advantages of this invention will become readily apparent upon a consideration of the ensuring specification.

According to the present invention there is provided a thread tensioning mechanism for a sewing machine comprising thread engaging means and means for applying a force to said thread engaging means which generates thread tension by providing resistance to movement of a thread therethrough in proportion to the force applied to said thread engaging means, a lever operatively connected to apply the force to said thread engaging means, magnetically interacting elements arranged to generate the force applied to said thread engaging means, one of said magnetically interacting elements being carried by said lever, operator influenced means shiftably supporting the other of said magnetically interacting elements for selective positioning relatively to the fulcrum of said lever to vary the thread tension.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more fully comprehended it will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. I is a front elevational view of a sewing machine having the present invention incorporated therein, portions of the machine frame being broken away to illustrate a tension release mechanism;

FIG. 2 is a perspective view of the thread tensioning mechanism of this invention with a removable top cover for the sewing machine depicted in phantom lines; and

FIG. 3 is an enlarged bottom plan view of a portion of the top cover for the sewing machine with a thread engaging head shown in cross section and the movable magnet means of this invention illustrated in two different operative positions.

DESCRIPTION OF THE INVENTION Referring particularly to FIG. I, the dial selector 17 of the thread tensioning mechanism is shown as being applied to the needle thread of a sewing machine having a work supporting bed 12 and a bracket arm 13 overhanging the bed and terminating in a sewing head 14. The bracket arm and the sewing head are hollow and are provided with an opening at the top adapted to be closed by a top cover plate 15 which is removable and may be fastened to the bracket arm by any suitable means. The cover plate serves as a common support frame for the needle thread engaging means 16 and for the tension regulating member 17.

US. Pat. No. 3,667,414, granted June 6, I972, discloses a preferred constructional arrangement for a thread engaging mechanism and a needle thread take up mechanism which does not detract from the operators view of the work being stitched and does not compete for the limited space available to the various mechanisms within the sewing machine. The thread tensioning mechanism of this invention is illustrated as being incorporated in a sewing machine in similar relationship with the take-up mechanism.

Referring further to FIG. 1, it will be seen that a reciprocatory needle bar 18 is journalled in the sewing head 14 and is provided with a thread carrying needle 19 secured adjacent its lower end by a suitable clamp device 20. The needle bar 18 and a needle thread takeup arm 21 having a thread eye 22 closely adjacent thereto are imparted reciprocatory movements in concert by a drive mechanism (not shown) located in the bracket arm.

The needle thread tensioning mechanism 23 (note FIG. 2) of this invention is carried by the removable top cover of the sewing machine frame in a position, as stated previously, where such mechanism does not detract from the operatorsiview of the work being stitched and where it does not compete for available space with the various mechanisms within the sewing machine. The needle thread tensioning mechanism includes a thread engaging means or head 16 which extends exteriorly of the top cover closely adjacent the path of movement of the take-up arm 21. Also projecting exteriorly of the top cover 15 is an operator influenced tension regulating dial selector 17 which, as will be described in greater detail hereinafter, serves for regulation of the tension imparted to the needle thread. As will be seen from FIG. 1, a needle thread N is directed from a supply spool (not shown) to the thread engaging head 16 and is subjected to the elements thereof, thence proceeds downwardly about a thread guiding post 24 which is set into the sewing head and may be formed with a thread detaining skirt 25. The thread guiding post is arranged beneath the path of motion of the take-up arm and eyelet 22 to which the thread is directed from the thread guiding post. From the take-up arm the thread is directed downwardly to the sewing machine needle 19.

Portions of the sewing head, the top cover 15, and portions of an end cover plate 26 have been broken away in FIG. 1 together with portions of the needle bar 18 and driving mechanism of the sewing machine in order to expose the basic elements and arrangement of a tension releasing mechanism 27. It is to be understood, however, that such tension releasing mechanism does not form part of the present invention and, therefore, will not be described in detail. For a more detailed description of this mechanism, reference is made to the aforementioned US. Pat. No. 3,667,414. Suffice to state that when the operator desires to relieve the tension on the needle thread the operator need simply move presser foot lifter lever 28. Through the linkage constituted by cam 36, block 37, rod 38, offset lever arm 39, tension release lever 40 and lever arm 41 (see FIGS. 2 and 3) the magnetic force-transmitting lever 42 is caused to pivot about its fulcrum and move towards the thread engaging head 16 in similar manner as the spring force-transmitting lever 110 of the aforesaid patent. Such movement of lever 42 results in the removal of the magnetically induced force from shaft 43 and thereby from the thread engaging discs of thread engaging head 16, so as to decrease the tension on the thread.

Thread engaging head 16 is illustrated in cross section in FIG. 3; however, since this device as such also does not form a part of the present invention, reference is made to the aforementioned US. Pat. No. 3,667,414 for a detailed description of its constructional arrangement. Briefly, a rod or shaft 43 is provided which is adapted to slide axially within the bore of a stud 45. Shaft 43 is given an enlarged head 46 at one end thereof and an enlarged head 44 at the other end. Enlarged head 44 is positioned on one side of a sidewall 47 of lever 42, and enlarged head 46 is located on one side of the outermost of friction discs 48, 49, 50. In this manner movement of shaft 43 in a direction away from thread engaging head 16 results in a corresponding relative movement of the friction discs towards each other so as to increase the frictional resistance imposed upon the needle thread passing therebetween. As described heretofore, under the influence of the presser foot lifter lever 28 the lever 42 is caused to pivot about its fulcrum to thereby swing that end of lever 42 adjacent thread engaging head 16 towards said head to relieve the pressure upon the friction discs and thus decrease the tension on the needle thread.

The needle thread tensioning mechanism of this invention will now be described with reference to FIGS. 2 and 3 of the drawings. It will be observed that the tensioning mechanism is carried interiorly of the top cover 15 in superposed relation to bracket arm 13 and in a space which is not ordinarily occupied by any of the usual operating mechanisms of a sewing machine. Lever 42 is formed ofa magnetically attractive material or carries a magnetically interacting element thereon, and is journalled in the top cover by a fastening stud or pivot pin 51. An aperture is provided in lever 42 through which stud 51 extends and is of sufficiently large diameter to permit pivotal movement of the lever thereabout under the influence of a magnetic force developed by a permanent magnet 52 such that stud 51 serves as the fulcrum for the lever. The lever is preferably planar and formed with an arcuate portion 53 desirably having a substantially constant radius of curvature, preferably extending circumferentially for approximately and with a relatively short straight portion 54 projecting substantially radially therefrom. As will be observed, the fulcrum of lever 42 is desirably located adjacent the juncture of the arcuate and straight portions thereof. One sidewall of the lever is preferably raised as at 47, and an aperture 55 is provided in the raised sidewall opposite thread engaging head 16 and is adapted to receive one end of shaft 43 with its enlarged head 44. It will be appreciated by persons skilled in the art that aperture 55 may be formed with a main section of sufficient dimension to permit the insertion of enlarged head 44 therethrough and with another section sufficiently large to accommodate shaft 43 but of smaller dimension than enlarged head 44. A spring clip or similar locking means, cooperable with shaft 43 and the adjacent walls of aperture 55 may be employed to lock the shaft within the smaller dimensioned section of the aperture and yet permit reciprocation therethrough.

Secured rotatably to the top cover by means such as stud or pivot pin 56 is a yoke-shaped member 57. A set screw 58 or the like may be utilized to operatively connect the base of the yoke member to the stud, thereby insuring rotation of the yoke member together with the stud. Within the bight of the yoke member there is positioned a permanent magnet 52 maintained in fixed position by means such as a set screw 59. On the outer side of the top cover dial selector 17 is affixed to stud 56 for rotation therewith. Associated with the dial selector, but not shown, is a scale which is calibrated to indicate a range of appropriate needle thread tension values. Thus, rotation of the dial selector to a particular tension value causes rotation of stud 56 and permanent magnet 52. This results in the development of a corresponding magnetic force moment about the fulcrum of lever 42.

Referring particularly to FIG. 3, it will be seen that the arcuate portion of lever 42 is formed with a substantially constant radius of curvature and that the permanent magnet 52 is adapted for rotation with stud or pin 56 such that in all of its rotative positions the longitudinal axis of the magnet will be substantially perpendicular to said arcuate portion of the lever. Preferably, the point at which stud 56 is journalled in top cover is selected such that the air gap between the end of magnet 52 and the contiguous surface of lever 42 increases as the magnet rotates in a direction decreasing the mechanical advantage of the lever. This enables an attenuation of the magnetic force at such locations of the magnet and the development of the maximum magnetic force at positions of the magnet where the mechanical advantage of the lever reaches its maximum. This is depicted in FIG. 3 by the position shown by dotted lines. However, it is. within the contemplation of this invention to so locate the stud 56 such that the arc of rotation adopted by the magnet will result in an air gap of uniform value throughout. Stops 60 and 61 may be provided for limiting respectively the extent of rotation of magnet 52 and the pivotal movement oflever 42 when same is under the influence of the needle thread tension relieving mechanism 27.

As is well known to persons versed in the art, calibration of the dial selector is generally determined in accordance with a particular thread tension vs. dial setting curve. Such curves plot thread tension values along the vertical axis and incremental dial settings along the horizontal axis. One such curve found to be eminently satisfactory plots thread tension values of from approximately grams at zero dial setting to approximately 700 grams at dial setting increment 10. It will be recognized, therefore, that as the upper range of dial settings is approached the curve tends to be asymptotic.

Depending upon the particular types of stitches to be performed by the sewing machine a curve may be developed which will afford the type of dial selector control desired. For example, at the lower thread tension values it is normally possible to obtain extremely fine tension control whereas in the upper range of thread tension values it is possible to obtain sharp increases in thread tensions per incremental dial setting.

The parameters for development of the desired thread tension vs. dial setting curve comprise (a) the mechanical advantage of the lever (which has generally been found desirable in the range of from 1:3 to 1:4), (b) the air gap (which may be determined from the magnetic force vs. air gap curve for the particular permanent magnet employed so as to provide the magnetic force desired), and (c) the range of moment arms for the arcuate portion of the lever. By a suitable selection of these parameters the desired thread tension vs. dial setting curve may be obtained. The scale for the sewing machine may then be calibrated in accordance with this curve. All sewing machines constructed so as to incorporate thread tensioning mechanisms designed to perform according to this curve, and provided with scales similarly calibrated, will reflect identical thread tension values on their scales. The dial selectors of all such machines will retain their accuracy since there is no dependence upon the usual spring elements to develop thread tension, and there is no extensive linkage system whereby play may be introduced through extended use of the machine.

Although the thread tensioning mechanism of this invention is disclosed as being carried by the removable top cover plate 15, it will be understood that the mechanism will function equally well if it were to be mounted upon a support member interposed between the sewing machine frame and said top cover plate.

Having set forth the nature of this invention, what is claimed herein is:

l. A thread tensioning mechanism for a sewing machine comprising thread engaging means and means for applying a force to said thread engaging means which generates thread tension by providing resistance to movement of a thread therethrough in proportion to the force applied to said thread engaging means, a lever operatively connected to apply the force to said thread engaging means, magnetically interacting elements arranged to generate the force applied to said thread engaging means, one of said magnetically interacting elements being carried by said lever, operator influenced means shiftably supporting the other of said magnetically interacting elements for selective positioning relatively to the fulcrum of said lever to vary the thread tension.

2. A thread tensioning mechanism for a sewing machine as set forth in claim 1, in which said operator influenced means defines a predetermined path of movement for said magnetically interacting element carried thereby, and in which that magnetically interacting element which is carried by said lever defines a lever arm contour which differs from the predetermined path of the magnetically interacting element supported by said operator influenced means such that movement of said operator influenced means changes the air gap between said magnetically interacting elements to vary the thread tension.

" 3. A thread tensioning mechanism for a sewing machine as set forth in claim 1, including a supporting frame in which the lever fulcrum is carried, said operator influenced means including a shaft journalled in said supporting frame on an axis parallel to said lever fulcrum axis, that magnetically interacting element which is supported by said operator influenced means being secured relatively to said shaft for movement along a circular path, and that magnetically interacting element which is carried by said lever defining a lever arm contour everywhere spaced from said circular path such that turning of said shaft changes the mechanical advantage of said lever to vary the thread tension.

4. A thread tensioning mechanism for sewing machines as set forth in claim 3, in which the contour of said lever arm defined by said magnetically interacting element which is carried by said lever differs from the circular path of movement of that magnetically interacting element which is supported by said operator influenced means such that turning of said shaft changes both the mechanical advantage of the lever and the air claim 4, in which said operator influenced meanssupported magnetically interacting element comprises a permanent magnet carried fixedly within the bight portion of a yoke-shaped member, said yoke-shaped member being mounted on a stud member journalled in said supporting frame.

7. A thread tensioning mechanism as set forth in claim 6, in which said supporting frame comprises the top cover plate of the sewing machine. 

1. A thread tensioning mechanism for a sewing machine comprising thread engaging means and means for applying a force to said thread engaging means which generates thread tension by providing resistance to movement of a thread therethroUgh in proportion to the force applied to said thread engaging means, a lever operatively connected to apply the force to said thread engaging means, magnetically interacting elements arranged to generate the force applied to said thread engaging means, one of said magnetically interacting elements being carried by said lever, operator influenced means shiftably supporting the other of said magnetically interacting elements for selective positioning relatively to the fulcrum of said lever to vary the thread tension.
 2. A thread tensioning mechanism for a sewing machine as set forth in claim 1, in which said operator influenced means defines a predetermined path of movement for said magnetically interacting element carried thereby, and in which that magnetically interacting element which is carried by said lever defines a lever arm contour which differs from the predetermined path of the magnetically interacting element supported by said operator influenced means such that movement of said operator influenced means changes the air gap between said magnetically interacting elements to vary the thread tension.
 3. A thread tensioning mechanism for a sewing machine as set forth in claim 1, including a supporting frame in which the lever fulcrum is carried, said operator influenced means including a shaft journalled in said supporting frame on an axis parallel to said lever fulcrum axis, that magnetically interacting element which is supported by said operator influenced means being secured relatively to said shaft for movement along a circular path, and that magnetically interacting element which is carried by said lever defining a lever arm contour everywhere spaced from said circular path such that turning of said shaft changes the mechanical advantage of said lever to vary the thread tension.
 4. A thread tensioning mechanism for sewing machines as set forth in claim 3, in which the contour of said lever arm defined by said magnetically interacting element which is carried by said lever differs from the circular path of movement of that magnetically interacting element which is supported by said operator influenced means such that turning of said shaft changes both the mechanical advantage of the lever and the air gap between said magnetically interacting elements to vary the thread tension.
 5. A thread tensioning mechanism as set forth in claim 4, in which said lever comprises an arcuate portion having a substantially constant radius of curvature and a projection extending substantially radially therefrom, said extension being adapted to operatively engage with a shaft included in said thread engaging means for transmitting said thread tension generating force thereto.
 6. A thread tensioning mechanism as set forth in claim 4, in which said operator influenced means-supported magnetically interacting element comprises a permanent magnet carried fixedly within the bight portion of a yoke-shaped member, said yoke-shaped member being mounted on a stud member journalled in said supporting frame.
 7. A thread tensioning mechanism as set forth in claim 6, in which said supporting frame comprises the top cover plate of the sewing machine. 